There is described a transmission (6) for a helicopter (1), the transmission having a movable transmission member (7); a casing (8) housing the movable member (7); lubricated supporting means (9) for supporting the movable member (7) inside the casing (8) and for rotation about an axis (A); and feed means (11) for feeding a lubricating fluid to the supporting means (9); the transmission (6) also has storage means (25) permitting gradual release of the lubricating fluid, and which are connected fluidically to the feed means (11) and to the supporting means (9) to permit lubrication of the supporting means (9) in the event of breakdown of the feed means (11); and the storage means (25) are angularly integral with the movable member (7) and located radially inwards of the supporting means (9) to feed the lubricating fluid centrifugally to the supporting means (9).